The present application is directed to energy production and, more particularly, to controlled hydrogen production.
Energy requiring equipment, including portable equipment, such as unmanned aerial vehicles (UAVs), communication devices, geo-positioning devices, sensors, and observation devices, among many others, rely on batteries or fossil fuels for power. In general, batteries are presently preferred over fossil fuels because they have zero emissions, are silent and they generally diminish the risk of explosion. Unfortunately, state of the art battery technology (such as Li-ion) has a much lower energy density when compared to fossil fuels. For example, the energy content of a 1 kg of Li-ion battery is only 0.15 kWh, which is ˜70 times lower than the energy content of 1 kg of gasoline. The weight and size of batteries also limits the usefulness.
Hydrogen gas can be used as a fuel without producing harmful emissions, and is theoretically the most energy dense and efficient fuel source (33 kWh/Kg). However, compressed hydrogen presents significant volumetric disadvantages, as well as safety and packaging challenges for implementation as a power source.
Another form of hydrogen fuel is that produced by the use of hydrides. In a first approach, chemical hydrides produce hydrogen gas by a chemical decomposition reaction which is thermally activated. Systems incorporating hydrides such as ammonia borane have been recently reported, such as in U.S. Patent Publication No. 20140178292 (Stephen Bennington et. al.). However these systems are disadvantaged because of the need to provide heat to activate the hydrogen production. It is very difficult to release all the hydrogen stored by this material. Particularly the release of the last molecule of hydrogen requires very high temperatures, above 400° C. (Celsius). The system design is further disadvantaged by the need to provide additional heater units which increases the system complexity. There is also a safety concern with the ammonia borane, as it releases hydrogen gas slowly even at low temperatures below 80° C., posing an explosion and fire risk to the user.
In a second approach, hydrogen gas is produced by the reaction of metal hydrides with water. The hydrogen generation capability of metal hydrides when reacting with water is outstanding. This system is beneficial when compared with the chemical hydride method because half of the hydrogen gas results from the metal hydride, while the other half comes from water that is reacted with the hydride. Water is generally easily available and is inexpensive when compared with metal hydrides. However, simply adding water to metal hydrides would be unsafe since their extreme reactivity with water could result in explosion and fire. Therefore they are not directly usable as a hydrogen release material. They are also unsafe to handle due to humidity sensitivity and other issues. One successful approach to stabilized metal hydride systems has been demonstrated with a sodium borohydide system. The stabilized system is provided as solution of sodium borohydride of a concentration of up to about 20% dissolved in water and stabilized by about 3% sodium hydroxide. Sodium borohydride does not react with water in the basic pH enabled by the hydroxide. The system generates hydrogen when activated by a catalyst. Unfortunately, hydride implementations have been very low in storage density, falling in the range of a few percent by weight at best, particularly because of the fact that the vast majority of the overall fuel weight is water. This large water requirement, along with other necessary equipment, increases the weight of the system and, again, is one of the reasons the energy density of a sodium borohydride system is low.
There is a need for a lightweight and safe fuel that may be used with energy requiring equipment including, but not limited to, portable type equipment.